Page Load Time (PLT) is critical in measuring web page load performance. However, the existing PLT metrics are designed to measure the Web page load performance on desktops/laptops and do not consider user interactions on mobile browsers. As a result, they are ill-suited to measure mobile page load performance from the perspective of the user.

In this work, we present the Mobile User-Centered Page Load Time Estimator (muPLT_est), a model that estimates the PLT of users on Web pages for mobile browsers. We show that traditional methods to measure user PLT for desktops are unsuited to mobiles because they only consider the initial viewport, which is the part of the screen that is in the user's view when they first begin to load the page.

However, mobile users view multiple viewports during the page load process since they start to scroll even before the page is loaded. We thus construct the muPLT_est to account for page load activities across viewports.

We train our model with crowdsourced scrolling behavior from live users. We show that our model predicts ground truth user-centered PLT, or the muPLT, obtained from live users with an error of 10-15% across 50 Web pages. Comparatively, traditional PLT metrics perform within 44-90% of the muPLT. Finally, we show how developers can use the muPLT_est to scalably estimate changes in user experience when applying different Web optimizations.